Abstract
Interspecific hybrids and constructed research models have provided infor-mation on intracellular interactions. We used two introgressed, chromosomally differentiated strains (H4 and H2) derived from F1 hybrids of crosses between D. prosaltans females and D. saltans males. In H4, the D. prosaltans chromosomes were eliminated. In H2, a mixture was maintained, preserving the entire genome of D. prosaltans (except the Y chromosome) and parts of the D. saltans genome. The IIR arm and a segment of chromosome III were eliminated. A third strain, used for comparison, was a normal D. prosaltans strain (P). This study aimed primarily to analyze the effect on the reproductive char-acteristics productivity (number of progeny) and sex-ratio caused by Wolbachia infection in interaction with different chromosome constitutions. For this, infected and uninfected flies were used in intrastrain cross combinations. Firstly, we analyzed the productivity of intracrosses of uninfected parents, in each strain, in order to detect the effects of intracellular interactions, in flies carrying different chromosome constitutions and sharing a Wolbach-ia-free, D. prosaltans cytoplasm. Data indicated that the chromosome parts that were eliminated, in H2, carry the isolating genes that impair productivity in hybrids of the two species, and suggested the occurrence of a nuclear/nuclear interaction. The analysis of Wolbachia-infected flies showed that the three strains presented different responses, depending on the chromosome constitution. As to productivity, the infection was harmful in P strain, in H2 behaved as mutualistic, and, in H4, produced the effect cytoplasmic incompatibility. As to sex-ratio, intracrosses showed significant differences in P and H4 strains. These results, associated with the cytological characteristics of the strains, pointed to the fundamental importance of host chromosome constitution to define the interactive process host/Wolbachia, and showed the flexibility of the endo-symbiont manifested in different forms of self-preservation.
Highlights
It has been known, for a long time, that interactions between nucleus and cytoplasm are essential for normal cell physiology
We analyzed the productivity of intracrosses of uninfected parents, in each strain, in order to detect the effects of intracellular interactions, in flies carrying different chromosome constitutions and sharing a Wolbachia-free, D. prosaltans cytoplasm
Considering that, unlike the nuclear genes, which are inherited from both mother and father, cytoplasmic structures and Wolbachia are passed on along the female line, it is expected that H2 and H4, which were originated from the same F1 progeny, share the same cytoplasmic constitution, including the same mitochondrial genome and the same Wolbachia strain originated from D. prosaltans
Summary
For a long time, that interactions between nucleus and cytoplasm are essential for normal cell physiology. Many basic cellular processes such as protein synthesis and maturation of DNA, RNA and proteins are dependent on these interrelations. The interplay for carrying out these processes and many others requires compatibility between nuclear and cytoplasmic material. Hybrids have often been successfully used to understand the intracellular interactions and their mechanisms. The characteristics productivity and viability are among the ones that are affected in interspecific hybrids. The harmful effects may be due to abnormal interplay nuclear-nuclear DNA, resulting from accumulation of genes that cause incompatible epistatic interactions between the species intercrossed. These genes were called speciation genes [1] [2] [3]
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